A Frog-Derived Cathelicidin Peptide with Dual Antimicrobial and Immunomodulatory Activities Effectively Ameliorates Staphylococcus aureus-Induced Peritonitis in Mice

Cath-HG improves the survival rates and symptoms in LPS-induced septic mice due to its multifunctional properties

The clinical syndrome of sepsis arises from severe infection, triggering an abnormal immune response that can lead to multiple organ dysfunction and ultimately the death of the host. Current therapies for sepsis are often limited in efficacy and fail to target the complex interplay of infection, inflammation and coagulation, leading to high mortality rates, which underscores the urgent need for novel therapeutics to combat sepsis. We previously identified Cath-HG, a compound capable of alleviating platelet dysfunction by suppressing GPVI-mediated platelet activation, thereby improving the survival of septic mice subjected to cecal ligation and puncture. Here, we further explored the antimicrobial, anti-inflammatory, LPS-neutralizing and anticoagulant properties of Cath-HG, as well as its protective effects in LPS-induced septic mice. Our results demonstrated that Cath-HG can bind to LPS, aggregate bacteria, and disrupt bacterial cell membranes, subsequently resulting in microbial death. Unlike most other Cathelicidins, Cath-HG displayed anticoagulation properties by regulating the enzymes plasmin, thrombin, β-tryptase, chymase and tissue plasminogen activator. In septic mice, Cath-HG provided protection against sepsis induced by LPS injection and exhibited bactericidal killing, LPS neutralization and inhibition of coagulation and MAPK signal transduction. Furthermore, Cath-HG obviously reduced the expression of pro-inflammatory cytokines and improved the pathological manifestations of tissue injury across multiple organs. Thus, Cath-HG emerges as a promising drug candidate for protecting against sepsis.

Novel casein-derived immunomodulatory peptide PFPEVFG: Activity assessment, molecular docking, activity site, and mechanism of action

Presently, there is a gap in the knowledge of the structure-activity relationship of immunomodulatory peptides. In this study, PFPEVFG was selected as a peptide with immunomodulatory activity from casein hydrolysate by virtual screening, and its immunomodulatory activity was verified by the phagocytosis, proliferation, and expression of cytokines (IL-6, IL-1β, TNF-α) and chemokines (CXCL1, CXCL2) in RAW 264.7 macrophages. Next, molecular docking and double-stranded small interfering RNA mutually verified that the immunomodulatory activity of PFPEVFG was mediated by TLR2 and TLR4. Furthermore, the highest occupied molecular orbital (HOMO) analysis showed that the C19=O20 site with a HOMO contribution of 32.22988% was its active site, and the phenylalanine, where the C19=O20 site was located, was its active amino acid. Finally, the combination of pathway inhibitors and western blot revealed that PFPEVFG activated macrophages through the nuclear factor-κB signaling pathway. In summary, this study provided a new perspective on deeply understanding the structure-activity relationship of casein-derived immunomodulatory peptides, as well as a further theoretical and technological basis for the application of immunomodulatory peptides.

New Insights into the Structure-Activity Relationship of a Novel Immunomodulatory Peptide (HPHPHLSF) from Casein Hydrolyzed by Kluyveromyces marxianus JY-1: Molecular Docking, Interaction Evaluation, and HOMO Analysis

Casein is rich in immunomodulatory peptides. In this study, the release of casein-derived immunomodulatory peptides by Kluyveromyces marxianus JY-1 was investigated for the first time, and an immunosuppressive mouse model was used to evaluate the immunomodulatory activity in the casein hydrolysate. The results showed that the cellular and humoral immunity of immunosuppressed mice could be significantly enhanced by casein hydrolysate. Peptide HPHPHLSF with high immunomodulatory activity from casein hydrolysate was screened using the virtual screening technique. HPHPHLSF possessed strong immunomodulatory activity and significantly upregulated the expression of IL-6, IL-1β, and TNF-α. Next, the interaction of HPHPHLSF with TLR2/4 on the cell surface of RAW264.7 cells was further elucidated by molecular docking and combined analysis of double-stranded small interfering RNA and receptor inhibitors. Further, the results of the highest occupied molecular orbital energy distribution elucidated that the histidine active site C48═O49 played an important role in the immunomodulatory activity of HPHPHLSF. This study confirmed that casein hydrolyzed by K. marxianus JY-1 was a natural immunomodulator, while the structure-activity relationship analysis provided new theoretical and technical support for the targeted preparation and screening of casein-derived immunomodulatory peptides.

Gastrointestinal digestion of food proteins: Anticancer, antihypertensive, anti-obesity, and immunomodulatory mechanisms of the derived peptides

Food proteins and their peptides play a significant role in the important biological processes and physiological functions of the body. The peptides show diverse biological benefits ranging from anticancer to antihypertensive, anti-obesity, and immunomodulatory, among others. In this review, an overview of food protein digestion in the gastrointestinal tract and the mechanisms involved was presented. As some proteins remain resistant and undigested, the multifarious factors (e.g. protein type and structure, microbial composition, pH levels and redox potential, host factors, etc.) affecting their colonic fermentation, the derived peptides, and amino acids that evade intestinal digestion are thus considered. The section that follows focuses on the mechanisms of the peptides with anticancer, antihypertensive, anti-obesity, and immunomodulatory effects. As further considerations were made, it is concluded that clinical studies targeting a clear understanding of the gastrointestinal stability, bioavailability, and safety of food-based peptides are still warranted.

Recent advances in the therapeutic potential of cathelicidins

The alarming increase in antimicrobial resistance in the last decades has prompted the search for alternatives to control infectious diseases. Antimicrobial peptides (AMPs) represent a heterogeneous class of molecules with ample antibacterial, antiviral, and antifungal effects. They can be found in many organisms, including all classes of vertebrates, providing a valuable source of new antimicrobial agents. The unique properties of AMPs make it harder for microbes develop resistance, while their immunomodulatory properties and target diversity reinforce their translational use in multiple diseases, from autoimmune disorders to different types of cancer. The latest years have witnessed a vast number of studies evaluating the use of AMPs in therapy, with many progressing to clinical trials. The present review explores the recent developments in the medicinal properties of cathelicidins, a vast family of AMPs with potent antimicrobial and immunomodulatory effects. Cathelicidins from several organisms have been tested in disease models of viral and bacterial infections, inflammatory diseases, and tumors, with encouraging results. Combining nanomaterials with active, natural antimicrobial peptides, including LL-37 and synthetic analogs like ceragenins, leads to the creation of innovative nanoagents with significant clinical promise. However, there are still important limitations, such as the toxicity of many cathelicidins to healthy host cells and low stability in vivo. The recent advances in nanomaterials and synthetic biology may help overcome the current limitations, enabling the use of cathelicidins in future therapeutics. Furthermore, a better understanding of the mechanisms of cathelicidin action in vivo and their synergy with other host molecules will contribute to the development of safer, highly effective therapies.

A Nonbactericidal Anionic Antimicrobial Peptide Provides Prophylactic and Therapeutic Efficacies against Bacterial Infections in Mice by Immunomodulatory-Antithrombotic Duality

Although bactericidal cationic antimicrobial peptides (AMPs) have been well characterized, less information is available about the antibacterial properties and mechanisms of action of nonbactericidal AMPs, especially nonbactericidal anionic AMPs. Herein, a novel anionic antimicrobial peptide (Gy-CATH) with a net charge of -4 was identified from the skin of the frog Glyphoglossus yunnanensis. Gy-CATH lacks direct antibacterial effects but exhibits significantly preventive and therapeutic capacities in mice that are infected with Staphylococcus aureus, Enterobacteriaceae coli, methicillin-resistant Staphylococcus aureus (MRSA), or carbapenem-resistant E. coli (CREC). In vitro and in vivo investigations proved the regulation of Gy-CATH on neutrophils and macrophages involved in the host immune defense against infection. Moreover, Gy-CATH significantly reduced the extent of pulmonary fibrin deposition and prevented thrombosis in mice, which was attributed to the regulatory role of Gy-CATH in physiological anticoagulants and platelet aggregation. These findings show that Gy-CATH is a potential candidate for the treatment of bacterial infection.

An amphibian-derived cathelicidin accelerates cutaneous wound healing through its main regulatory effect on phagocytes

Cathelicidins are an important family of antimicrobial peptides (AMPs) involved in the innate immunity in vertebrates. The mammalian cathelicidins have been well characterized, but the relationship between structure and function in amphibian cathelicidins is still not well understood. In this study, a novel 29-residue cathelicidin antimicrobial peptide (BugaCATH) was identified from the skin of Bufo gargarizans. Unlike other AMPs, BugaCATH does not display any direct antimicrobial effects in vitro. However, it effectively promotes full-thickness wound repair in mice. Following injury, BugaCATH initiates and expedites the inflammatory stage by recruiting neutrophils and macrophages to the wound site. BugaCATH not only regulates neutrophil phagocytic activity but also stimulates the generation of cytokines (TNF-α, IL-6, and IL-1β) and chemokines (CXCL1, CXCL2, CCL2, and CCL3) in macrophages and in mice. Furthermore, it promotes macrophage M2 polarization that facilitates the conversion from a pro-inflammatory macrophage-dominated wound environment to an anti-inflammatory one during the mid to late stages, which is crucial for reducing inflammation and effective wound repair. The MAPK (ERK, JNK, and p38) and NF-κB-NLRP3 signaling pathways are involved in the activity. Moreover, BugaCATH directly enhances the migration of keratinocytes and vascular endothelial cells without affecting their proliferation. Notably, BugaCATH significantly improves the proliferation of keratinocytes and endothelial cells in the presence of macrophages. The current study revealed that in addition to proliferation of keratinocytes and endothelial cells, BugaCATH possesses the ability to modulate inflammatory processes during skin injury through its regulatory effect on phagocytes. The combination of these capabilities makes BugaCATH a potent candidate for skin wound therapy.

Chensinin-1b Alleviates DSS-Induced Inflammatory Bowel Disease by Inducing Macrophage Switching from the M1 to the M2 Phenotype

Inflammatory bowel disease (IBD) is a chronic relapsing inflammatory disorder with an increasing prevalence worldwide. Macrophage polarization is involved in the pathogenesis of IBD. Repolarization of macrophage has thus emerged as a novel therapeutic approach for managing IBD. Chensinin-1b, derived from the skin of Rana chensinensis, is a derivative of a native antimicrobial peptide (AMP). It shows anti-inflammatory effects in sepsis models and can potentially modulate macrophage polarization. The objective of this research was to study the role of chensinin-1b in macrophage polarization and dextran sulfate sodium (DSS)-induced colitis. RAW264.7 macrophages were polarized to the M1 phenotype using lipopolysaccharide (LPS) and simultaneously administered chensinin-1b at various concentrations. The ability of chenisnin-1b to reorient macrophage polarization was assessed by ELISA, qRT-PCR, and flow cytometry analysis. The addition of chensinin-1b significantly restrained the expression of M1-associated proinflammatory cytokines and surface markers, including TNF-α, IL-6, NO, and CD86, and exaggerated the expression of M2-associated anti-inflammatory cytokines and surface markers, including IL-10, TGF-β1, Arg-1, Fizz1, Chil3, and CD206. Mechanistically, via Western Blotting, we revealed that chensinin-1b induces macrophage polarization from the M1 to the M2 phenotype by inhibiting the phosphorylation of nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK). In mouse models of colitis, intraperitoneal administration of chensinin-1b alleviated symptoms induced by DSS, including weight loss, elevated disease activity index (DAI) scores, colon shortening, colonic tissue damage, and splenomegaly. Consistent with our in vitro data, chensinin-1b induced significant decreases in the expression of M1 phenotype biomarkers and increases in the expression of M2 phenotype biomarkers in the mouse colitis model. Furthermore, chensinin-1b treatment repressesed NF-κB phosphorylation in vivo. Overall, our data showed that chensinin-1b attenuates IBD by repolarizing macrophages from the M1 to the M2 phenotype, suggesting its potential as a therapeutic candidate for IBD.

Tree Frog-Derived Cathelicidin Protects Mice against Bacterial Infection through Its Antimicrobial and Anti-Inflammatory Activities and Regulatory Effect on Phagocytes

Due to excessive use or abuse in the food industry, agriculture, and medicine, many pathogens are developing resistance against conventional antibiotics. Antimicrobial peptides (AMPs) hold promise as effective therapeutic options for the treatment of bacterial infections. Herein, a novel cathelicidin antimicrobial peptide (Zs-CATH) was identified from the tree frog Zhangixalus smaragdinus. Zs-CATH mainly adopted an amphipathic β-sheet structure in a membrane-mimetic environment. It showed broad-spectrum antibacterial activity against Gram-positive and Gram-negative bacteria in vitro and significantly protected mice from lethal infections induced by Gram-negative bacteria Escherichia coli ATCC 25922 or Gram-positive bacteria Staphylococcus aureus ATCC 25923 in vivo. In addition, Zs-CATH exerted a strong anti-inflammatory effect by neutralizing lipopolysaccharide (LPS) and lipoteichoic acid (LTA) and promoting macrophage M2 polarization, thus inhibiting the secretion of proinflammatory cytokines (TNF-α, IL-6, and IL-1β) and enhancing the production of M2 macrophage markers IL-10, IL-4, and CD206. The MAPK and NF-κB inflammatory signaling pathways and transcriptional activator 6 (STAT6) were involved in this effect. In mice, Zs-CATH rapidly recruited neutrophils and monocytes/macrophages to the abdominal cavity but not T and B lymphocytes. Zs-CATH did not exhibit a direct chemoattractant effect on phagocytes but significantly promoted phagocyte migration in the presence of macrophages. Zs-CATH stimulated macrophages to secrete chemokines CXCL1, CXCL2, and CCL2, which mediated the recruitment of phagocytes. Furthermore, Zs-CATH promoted the production of reactive oxygen species (ROS) and neutrophil extracellular traps (NETs), which are oxygen-dependent and oxygen-independent mechanisms of the microbicidal activity of neutrophils, respectively. Zs-CATH exhibited no toxic side effects on mammalian cells and mice. These findings show that in addition to direct antibacterial activity, Zs-CATH also possesses the ability to modulate immune and inflammatory processes during bacterial infection, showing potential for development as anti-infective and/or anti-inflammatory agents.

The Contribution of Antimicrobial Peptides to Immune Cell Function: A Review of Recent Advances

The development of novel antimicrobial agents to replace antibiotics has become urgent due to the emergence of multidrug-resistant microorganisms. Antimicrobial peptides (AMPs), widely distributed in all kingdoms of life, present strong antimicrobial activity against a variety of bacteria, fungi, parasites, and viruses. The potential of AMPs as new alternatives to antibiotics has gradually attracted considerable interest. In addition, AMPs exhibit strong anticancer potential as well as anti-inflammatory and immunomodulatory activity. Many studies have provided evidence that AMPs can recruit and activate immune cells, controlling inflammation. This review highlights the scientific literature focusing on evidence for the anti-inflammatory mechanisms of different AMPs in immune cells, including macrophages, monocytes, lymphocytes, mast cells, dendritic cells, neutrophils, and eosinophils. A variety of immunomodulatory characteristics, including the abilities to activate and differentiate immune cells, change the content and expression of inflammatory mediators, and regulate specific cellular functions and inflammation-related signaling pathways, are summarized and discussed in detail. This comprehensive review contributes to a better understanding of the role of AMPs in the regulation of the immune system and provides a reference for the use of AMPs as novel anti-inflammatory drugs for the treatment of various inflammatory diseases.